Oscillator



June 8, 1948'. P. wEATHl-:Rs

OSCILLATOR Filed DGO. 1l, 1946 MODULRTON OUTPUT MODULATIDN SOURCE ISAQ FREQUENCY IN KILOCYCLES fanununnix RR mm DD ET. .ww E VA. FF D NE o I 7., m w 44 n L L C U. ma A wm m P MM wf, @me n@ .f....m@ mmwmww w LW MODULNHGN SQURCE TTORNEV Patentecl June 8, 1948 OSCILLATOR? Paul Weathers,` Haddon Heights, N. J.assigno'r to Herbert K. Neuber, Philadelphia," Pal.'

Application Decenfiberl 11, 1946;SerialfNo.fl715,377

pled with -theoscillaton and includes the control ofA feedback currents differentially tov eiect an accentuated variationy in the'bias potential applied to the grid of 'theoscillator at the modulation frequency rate. This yresults in an enhanced variation in anode current and in themodulation-output signal derived from such variation.

It is anv object ofv the present invention, to provide an improved method and means -for `controlling an electronic-tube oscillator of` the selfexcited type by-modulation, whereby a/greatly amplied modulation signal may be derived therefrom in response-to extremely small changes in Capacity,l inductance or resistance in a control circuit coupled with the oscillator, and without applyingthe modulation signal to the grid of the f oscillator.y v

It is also an object of the present invention, to provide an improved electronic-tube oscillator system of the self-excited, modulatedtype refer-red tonvherein the modulation control effect thereon and the modulation voltage or signal output is of high fidelity and greatlyincreasedibeyondvalues heretofore attainable.

It lis a further object of this invention, to provide a self-excited, electronic-tube oscillator system'hav-ing a modulation control circuity for varying feedback from, vthe plate circuit to? the grid circuit, in-phase and counter-phase with respect to a normal feed-back for maintaining oscillations, which `provides an accentuated variation in the input capacity of the oscillator and a resulting variation in the tuning of the oscillator grid circuit, thereby to vary the'rnagnitude or strength of the oscillations without vappreciably varying the'freq-uency of the' oscillationsproducedywhereby a greatly/'increasedhigh fidelity modulation signal output is attained.

It has-been'found thatA a system of this type may produce a voltage variation or modulation signal'. oompOnentat theoutput-or anode circuit, ofrgreaterfmagnitudeand higher iidelity than has-heretoforevbeen possibleV with the oscillator systemreferredto and with the same relatively small variation of capacity, resistance or inductance' in thecontrol circuit. v It is also therefore, Well' adapted for use in -high fidelity phonograph record reproduction systems.

Themodulation-Usource-may comprise a small, light-Weight; push-pull-varlable capacitor or any variable impedance-and the oscillator and associated 'circuits-may becoupled thereto through a transmission line of appreciablelength, without introducing undesired modulationeilects and without appreciably limiting-the frequency range of response of-the impedance-element, or the amplitudeof'fthe controllingl effectv upon the o'scillatorandf-the'=delity of they resulting signal output" therefrom. l

It'is, therefore, a still 4further object of this invention, to provide an improved,selfexcited, electronic-tube.v oscillator system which `operates to Vary thefeed-back of energy from the anode circuitto the` grid circuit without appreciably varying lthe-frequency ofoscillation and Wholly in a condition of under neutralization responsive to variations in the input admittance ofthe tube.

i The veiectof 'variation input admittance or capacityyof the-type referred-tdisshoWn in Teryman-Radio Engineers -Handbook, 1943, Mc-

Graw-Hill Book Company, pp. 467 et seq. and in Figure92yon page 470.

lilltlfxer in;I accordance with the invention, the variation in Hinput capacity `or admittance is caused,` to be amplified or accentuatedand to produce'amampliedcontrolling effect upon the anodeV current in the output'lcircuit of lthe oscillator from which the modulation signal-component is derived.

The modulation source is Acoupled to the oscillator ythrough a .balanced-ito-cathodey or ground transmission Kline or control circuit which is eX- tremelynsensitive Yto capacity, -inductance or resistance changeset itsterminal-end, and operates to `control the flow of energy-fromthe anode circuit tothe grid circuit ofl the oscillator by differentialvcontrolof the coupling. In this manner a greatly increased: variation in anode current'ior youtputpotential is provided and a relatively: :great f-modulation leiect'` is produced upon the` oscillator'y in response' to relatively minute variations 'in' capacity, inductance or resistance at the' terminal end offthe control' circuit.

In a preferrednembodiment of the invention, having a modulation `-control cir-cuit above deof but slightly higher than that of the oscillator.

This response or resonance frequency varies with modulation, but has little eifect'onA the oscillator frequency. Thus with asy'ste'm' embody' ing the invention, variation in the inputV capaciational bias on the tube in response to oscillations. The cathode is connected to ground for the system as indicated at 22 and through a lead 23, and grid 1 is also connected to ground and to the lead 23 as indicated by the connection 24.

The capacity represented at Il comprises the sole tuning capacity for the input circuit 9, and accordingly theinductance element I9 maybe made relatively high in inductance value, and the variable tuning or adjustment of the initial frequency response of the circuit 9 is accomplished by varying the inductance Il), preferably by a movable tuning core 25 which may be of ferromagnetic or other suitable material.

tance of the oscillator merely varies the response provided on the grid circuit to vary the amplii tude of oscillations and the relative resonance frequencies of th'egrid and anode circuits by revilected reactance. Y

Viewed in one of its aspects, the modulation control -circuit may be considered to vary Athe feed-back or degree of neutralization of the oscillator, thereby to vary the input admittance or capacity, and the strength of oscillations to a high degree, in response to small variations in the impedance of th'e control circuit effected by the modulation source. f

The invention will, however, "be more fully understood from the following description when considered invconnection with the accompanying drawing, Vand its scope will be pointed out in the appended claims.

In the drawing: a

Figure 1` is 'a vschematic circuit diagram ofV an electronic-tube, modulated oscillator systemv embodying th'e invention in a present 'preferred form; 1

Figure 2 is a further schematic circuit diagram of an electronic-tube, modulated oscillator system embodying the invention; and showing a modiiication of the circuit of- Figure 1; and

VFigure 3 is a graph showing curves illustrating certain operating characteristics of the circuit of Figure 1;

Figure 4 is a still further schematic 'diagram of a portion of th'e circuit of Figure 1, arranged as a self-contained unit detachable and independent of the remainder of the system :and the oscillator tube, and adapted for plug-in connection therewith, as in the circuit of Figure '1. l Referring to'Figurel l, 5 is an electronic oscillator tube of the thermionic type having anv anode 6, a control grid 1 and a heated cathode 8. Between the grid and the cathode is connected a tuned grid -circuit 9 comprising a variable tuning inductance I9 and shunt tuning capacity indicated at` Il, the latter comprising mainly the reected grid-to-plate or anode capacity-Cyp, of the tube, together withV stray capacity andthe grid-to-cath'ode capacity of the tube.

A grid resistor l2 and grid capacitor 20 are connected in the grid circuit 9 for maintaining oper- A similar tunable circuit 2B is connected between the :anode and. ground, and comprises a variable tuning inductance 21 connected to the anode through a circuit lead 28 and to cathode and ground through a circuit lead 29 and a bypass capacitor 39. The shunt tuning capacity for the circuit 25, schematically indicated at '32is provided by the plate-to-cath'ode and plate-togrid capacities of the tube butl mainly'by a reflected reactance through the inductance 21 to the circuit 26. As in the case of the grid circuit, the anode circuit frequency response or tuning may be adjusted to a desired resonance by varying the inductance 21, by means of a suitable movable tuning core indicated at 33,

Anode current is supplied to the oscillator from a positive supply lead 34 through an output coupling impedance or resistor 35 `and the inductance 21, theresistor 35 beingconnected at 36, between the bypass capacitor 33 and the inductance 21. The supply lead 34 is also provided if desired, with a suitable bypass or filter capacitor` indicated at 31.v A modulation oraudio frequency signal output terminal, indicated at 38, is connested with the anode circuit at 4l on the high potential side lof the output coupling impedance 35, through a couplingycapacity 39 an-d a filter impedance 49 in series The opposite terminal of the output circuit is indicated at 42 and is connected to ground and cathode as indicated. This arrangement provides for deriving signal output at the modulation frequency across the impedance element 35 as the result of anode cur-` rent variations at the modulation frequency.

vWhen the grid and anode circuits 9 and 26 are resonated at different frequencies of the same order or value, by adjustment of the respective tuning cores Ill and 33, the tube 5 will oscillate because of energy feedbackracross the high inductance 21 through the grid-to-plate capacity, Cgp, from the circuit 2E to the circuit 9. When the tube oscillates, the anode current'low through the resistor 35 decreases becauseof an increase in negative bias on the oscillator gridr 1 established by the grid current flow through the :grid resistor l2, until a steady state ofoscillation is established. The oscillator is thus self-excited andtends to oscillate at a fixed frequency determined largely by the circuit constants inthe anode circuit. v

Feed-back from the anode circuit to the grid circuit lis produced through external means comprising a feed-back inductance 44 coupled to both the grid circuit and the anode circuit.

A coupling connection vfrom an intermediate point or center-tapV l5 thereon is provided, by means of which it is Vcoupled to the grid circuit 9 through a connection lead 46 terminatingwith a Vconnection 41 with the high potential Ior grid side of the grid'circuit 9. The tap 45 is preferably at the electrical or inductive center of the 'winding 44. On the anode side-of the coupling,

the feedback inductance 44 is closely coupled electromagnetically with the inductance 21 'in the anode circuit, whereby feed-back current or energy from the anode circuit may flow therelthrough to the grid circuit.

Means are also provided'in connection with the feed-back inductance for conveying feed-back current or energy from the anode circuit through said inductance differentially, to provide diiferential in-phase and counter-phase inductive feedback of energy to said grid circuit thereby to vary the amplitude or strength of oscillations of the oscillator and to control the relative resonance frequencies of the circuits connected with the inductances I0, 21, and 44 by reflected reactance in the anode circuit and input capacity variation, as will hereinafter be described.

The terminals 48 and 49 of the feed-back inductance 44 are connected to a transmission line forming part of the oscillator modulation control circuit, and comprising a pair of closely associated insulated leads 50 and 5|, preferably twisted together, and enclosed within a conducting shield 52, which is connected to the cath-ode return lead and ground of the oscillator through suitable ground leads indicated at 53 and 54.

A substantially iixed capacity is provided in connection with the terminals 48 and 49 by the leads 50 and 5|. This capacity is effectively connected in parallel with the feed-back inductance 44 as indicated by the dotted capacitor 55, thereby serving to tune the inductance 44 to a predetermined frequency.

The shield element of conduit 52 surroundinsr the leads 50 and 5|, provides additional tuning capacity effectively in parallel with the feed-back inductance 44. This is the stray capacity between each of the twisted leads of the cable and the shield element 52, the components of whichv are indicated at 51 and 58.

The value of the shunt capacity 55 remains substantially fixed in response to shifting of the cable in the shield or movement with respect to the Isystem ground and cathode connection. This however, changes both of the capacity values indicated at 51 and 58 substantially equally and in the same sense. Therefore, the overall change in capacity balance is effectively zero and no apprecable modulation or noise'effect is produced upon the system.

The terminal end of the transmission line is connected to variable control means or a modulav tion source providing inversely variable imped ance paths to ground or cathode for the control circuit leads 5U and 5| The modulation source shown in the present example is a push-pull variable capacitor having lixed electrodes or plates 60 and 6| connected with the terminal ends of the leads 50 and 5|, respectively. A movable I electrode or plate 62 is located between the fixed plates and pivoted as indicated at 63, for oscillation betwen said fixed plates to vary the air gaps on each side thereof inversely and correspondingly to vary the electrical impedance of the circuits connected with the fixed plates 5|) and 6| to ground or cathode. In the present example the plate 62 is actuated by suitable movable stylus means indicated at 54, The electrode 62 is preferably located substantially midway between the plates 6|! and 6| in a normal condition of rest and is connected as indicated, to the lead 54 for completing a circuit path through the capacity or impedance of the modulation means to ground of the oscillator system,'as shown.

'may be extended to'a considerabl'edistance without appreciably increasing the'capacity 55 between the leads beyond that which is required to resonate the .anodeinductance 21, by reflected reactance through the feed-back inductance 44, within a desired frequency response range. This range is determined -by the desired operating frequency of the oscillator.

4It will be seen therefore, that the feed-back inductance 44 is provided at its terminals with balanced feed-back paths to ground or cathode which provides a balanced positive and negative feed-back through the feed-back inductance which may be varied differentially to modulate the oscillator. l'lull modulation control of feedback through the inductance Mto the grid circuit may be realized by the use of a relatively small capacity change such as provided by a movable metallic reed at 62 of relatively small dimensions, when vibrated at relatively low amplitude between similar small electrodes at v5l) and 6|, although said electrodes may be relatively widely spaced.

To provide such small capacity or impedance change for controlling large and effective feedback of energy the feed-back inductance 44 is tightly coupled to the anode circuit inductance 21 whereby the reactance of the circuit connected therewith is reflected over into the anode circuit 26 and serves to tune the same to the desired frequency of oscillation for the oscillator. Furthermore, the exchange of energy from the anode circuit 25 to the grid circuit 9 upon slight movement of the controlling lelement at the modulation source is caused to be highly effective because of the resonance condition existing between the two circuits. It will be seen that as the flow of energy or current with respect to the tap 45 through one winding portion increases the flow through the other winding portion decreases proportionately thereby enhancing the control action or modulation range for push-pull action.

The oscillator circuit may utilize a high-mu triode tube such as a commercial type 6SF5 or GSQl inthe simplified form of the circuit as shown. Furthermore, all inductances such as l0, '21, and 44, also hereinafter referred to and designated in the drawing at LI, L2 and L3, respectively, may have essentially the same inductance and therefore may be the same electrically and physically, and be wound to the same diameter and size, for low cost manufacture.

The grid inductance LI is `tuned by the gridto-plate capacity Cyp of the tube at as hereinbefore referred to, plus the capacity of the inductance element L3 to ground, since `the latter is connected directly with the grid circuit 9 through the connections 46 and 41. In addition, the capacity to ground, 51 and 58, of the attached leads or control circuit 5il5|, aifects the tuning of the grid circuit 9, by reason of the same connection.

The inductance L3, that is the feed-back inductance, is tuned by the capacity 55 of the control circuit leads in shunt therewith. Variation in tuning response of the circuit 2li may be effected by movementof the tuning core 33, as hereinbefore pointed out. In the circuit 26 the anode circuit inductance 21 may be considered to be substantially untuned, but by reason of the close coupling with the inductance L3, and adjustment of the core 33, it is resonated at the desired oscillator frequency by the reected re- 'a'ctance Ifrom `the control I circuit and lL() over into .theianode 'circuit at 32.' l

".'fIhe 'oscillator'becomes :self oscillating ,fata (predetermined operating frequency, hereinafter yref'er'red 'toas `fl by 'the relatively :high anode inductance f-provided at -217 which 1causes feed-back .fromtheanode circuit to the grid circuit through fthe normal :plate-'toegridfcapacity Cyp. The Aan- :ode'circuit Iin the present example lmay be considered to be tuned to .an foperating frequency, ffl, for the oscillator,.oftheiorderof 1445kc. The ffeed-lia'ck :circuit fof L3 -rmay 'be considered Vto be 'tuned 'for vresponse at a frequency 1f3, "which -may 'be-of the 'order-.of f1'585 kc; in thefpresentexample 'The 'grid circuit ais tuned for lresponse at a i higher .frequency 'whichmay Ebe designated as J2, 'and may `be considered, yby way of example, `to lbe of the rorderzof '1570 11m. Thus 'both .thegri'd circuitrresponse frequency and the operating frequencycf the.anode'circuitare'of thesame order, Withithe gridfcircuitihavingfa slightly higher fre- 'quency response than the. 'oscillator .operating :fre-

quency.`

"Ihelancde circuit .iin'ductancezLZ further may be considered as a high inductancefcoil 'tuned vto :resonance by fthe associated rceqoacities 'and freected vre'actance and in series 'between Y:the r'ano'cle fand the vmodulation f'output circuit. '.Beingtightly yccuplecl iinductively to the feed-back finductan'ce 1.13, :which l-i-s lin Althe :modulation `control circuit, the reflected capacityorireactance :at 32 of L3 across L2, AtunesfiLz to ,the r:frequency fl (1445 km) and v'establishes l.the ioperatingffrequency Afor the osciliator.l 'Withthis arrangement .ithaswbeen found that variation-:cf xthe :tuning of -the lgrid circuit` :9 and roi Ll fhas substantially no effect upon the `isithe .operating'frequency Jil `andiis .minimum in the `regionof 1585 kc'whichfisthe adjustedlresomance frequency f3 -of the Ifeed-back".inductance and associated circuit .leads This `.provides a rmaxirnum feedibackfof :energy `from plate -togrid,f'f

r`and maximum oscillationfstrength at Vthe foscillator operating AfrequencyJ fr! -of A1445 rhe. The

' impedance-of the gridcircuitinductance -i-s-indicated by thecurve 6 linf-liligure, Yfor a-steadystate :condition -of oscillation. t rwill -be vnoted that .this resonance cr impedance-curve ris spaced in frequency above 4the operating Afrequency-jl. -It has been found'that the inductance Li of the grid circuit must `always be -tuned .for response at 'a ifrequency 72 above -frequency f-i for proper operationof the rsystem, as will. hereinafter -be described. l

The operation of the .system -is as follows: Assuming the oscillator to be energized,=theanode -circuit 26 is tuneduis-hereinbefore/pointedout to the normal-operating frequency, 3! and .the Agrid circuitA 9 is tuned afor-response-or yto resonatefat a `higher ffrequency, J2, -Which 4is of the .order of -or higher than the-frequency fl. Feed-back of energy from the anode-.circuit through-the normal .fgrid-to-anode capacity `path' maintains the osciliator in a -steadyv-stateof oscillation-'at `the fre- -quency 'fL The .average ianode current flowing through the output coupling .impedance $5 .assumes va const-ant normal'value, and `With Vsubsource. f

stantially no Variationinaverage. anode current, the `modulation .signal .output at theviterminafls 38 ands? is zero. .Radio :frequency .energy-.from Ithe .anode circuit is-prevented fromI appearingat the output yterminals by reason .ofthe bypass capacitor 30 and the impedanced connected .with terminal .38. y

. Feedebackcurrent or `energyfat -the ,frequency of the'tuned'anode circuit 26, owsvby-inductive coupling -through the feed-back Windinggi sub.- stantiallyequallycn either side of the .intermediate tap 45. Feedebackcurrent.ofenergy :may be consideredtofiow in -a-path which mayrrfbe traced .from :the 'terminal -45- rthrough the connec- .tion ..46 .and thergrid circuit inductance 1.0, thence through the ground connection and .the movable electrode 52, rthence through the electrodes `Bil and 6I, the cablezconnectionstt-.andaiback to ,theterminals 48 and 4S ofthe inductance-M.

'It IWill be seen that when `the ,controlcircuit .through lthe leads v5t 'and 5| and .themodulation .source til, t! and-@Sis balanced, -that 'is when 4and .differentially :a /fioW-of virl-@hase hor counterphase feedeback energyito the grid circuitthereyby -increa-singor decreasing `the strength ofioscillations.

This .is by :reason of the .-fact -that-Whenfthe feed-back of `energy `through the feed-back -inductance del is Variedffan increasein .feed-back from the/anode vcircuit .in one direction willraid, and in the opposite .direction will \oppose,..the normalvfeedf-back from `plategto grid Aby in-phase and counter-phase action. Therefore, simplified and effective .means are Aprovided Vfor conveying 4feed-.back current from theanode circuit-through the.feed.back .inductance differentially, .thereby .Varying the amplitude of oscillationsand :the signaloutput response .to .modulation .controlof the variable impedance means atthe .modulation Considering athe effect .of the feed-back lVaria- -tionas avariationin neutralizaticnof .the oscil- 155 -lator, .in response `to Variations` .in` yfeed-'.baclz vthrough'thefinductance M responsive tooperaftion'of the modulation source, it'willybe-seensthat 'feed-back finone direction will increase, -an'd :fin lthe opposite direction will decrease,` the fcondi- -tion of "neutralization, and the effective input eect upon the response frequency vof the grid circuit. Likewise, `as the v`effective input capacity '-decreases, the resonance frequency ofLhWillining v`frequency fl YW. ich Casethe magnitude or amplitude. ofthe oscillations WilL decrease.

In either rese, the change is ruches, tenente the. oscillator to build up an amplincation ofgthe change or to enhancethe effect. of yariatio'n of f eedfback, and therefore provides active r dynamic response to the modulation controliri either' 'direction of change to a greater degree and more effectively thanhas heretofore been possibile.

seen thatLl must be sufficiently tuned above 1,2 in frequency, or, above the operatinajfrequency of L2,A to. permit full modulaticnfwithout "appreaehing closely tothe frequency .of :fi :This is for the reason that it has been foundthfat when Llvr is tuned too closely to L2 in frequency response, oscillations at the modulationjirequency will take placeand this appearstobe, causedby Ll Shifting in tuning at the modulation-frequeny.

tieular-ly .the input .Capacity Component thereof, isfimnortenee, since the tube is operated .in Whetmny be .considered to ..be en fnnder neutralized state, and is Causedtooperate with a variable input capacity in turn Cnlliilgt attuariation inneutralization, in accordance with'the characteristics [described ini the, publication hereinbeiorelreferredto.

, Mariation of the;impedaneeelements atgthe the oscillator tube in -response to differential variations -Qf-feed-back -ifrom-the `anode ycircuit to the grid; circuit--with-respect -to -the lnornfial feed-back fory a'steady state;- self-excited condi- 5 tionof oscillation, While-the-anodecireuit tuning maintains a- -consta-nt -frequencyofoscillation.

The -yoltage drop --across the --series anode or plate impedance-);354 is--correspondingiyvaried- 4at the modulation frequency and --the modulation yl0 component ofthe signalis derived across-said impedance through '-theelter---impedance- '40- yand the coupling capacitor-39.- 'The-modulationsgnal output may -thenbe applied to `any sui-table utilization mean-s; not -shoWn-,- fromthe terminals esame-42.

In'A the transfer nor energy from the anode-circuit ',tothe-grid circuit it shouldbe noted that the lYbypass; capacitor- 30- -also'- provides a low I-impedanoe path for the" R. F.-energyfeed-back through ythel cathode circuit-to permitmaximum The grid. admittance/Loi theoscillatorpartransfer of f energy-trom -lthe- -anode---to Athegrid.

g-A further- --f-unction ofthis capacitor,- --n conjunction iWilthfthe impedanceelement 35; --is v-to provide al-otypassfilter for;alljdesiredmodulation g5 frequencies-havingagris-ingfrequency -characteristie-at the highf-requency-end ofthe-modulation frequency range and just betere-modulation .frequen-cycut off.' -This` is effected by the Acombination 4ofapa-cityand resistance in the plate circuit Aati-tins poi-nt -andit is-preferable-that-the terminals .of the control circuit,4 in thispase, ld ifferential Ivariation in ,C .ainacity 4 between the greund land the control circuit of, 4the Ained.-beek inductaneeJ-M, maybe-considered tQauSe ilariationinthe statepf neutralization of the osciltime constantl of' theflterarrangementbe--such `tlrrathigli frequency accentuation-takes `place just befpre high frequency olf.

f Inthe systemdescribe-@the grid Vcircuit inductance LI isn-ot inductively-associated-Witn-the-inlator, as the, impedanceot the co ntrol circuit e through one 4portion or, the other of thejfeedbaek induetenee Mis, varied .Withlresneet tothe tenter-tap conneetion 45 for :the grid eireut- The normal stateA of neutralization and the ductance L2 and L3.-^-It-may -be--connected-permanently in; the -gridfcircu-it and may be Vassociated with'g-the oscillator-system, whereas the inductance elernents-l'iZ and-Lit; bei-ng vclosely cou- 40 pled, may be main-tainedseparately-andspaced nignimpedaneeriate .circuit nautesteadystate 'f eseillatinna to bev maintained heweyer, and the state .Oi .neutralization is caused, to aprirne-entend renedef-fromthe range, of, over nentra1 izatic .n, l and .thereby tenses .the input napacityacrnea negri@ cireuitinduetanee Lilie vary .Il "nsyariationfis indicated by the. error/.associated WitntheQe- A matic Capacity l I.

Summarizing the foregoing description of the .Qnerationilhe Strength or niaenitudeni estilrespect tof the normal feedebacl; Awhich lestabvariation inthe input `capa-city 'of -the---tube-as Therefore variation- 0f thetunins Ofythe grid yariesthe magnitude 0r strength Of'the oseilleto n s, Hence, in 'this system, modulation is-"eff ectedby varyingfthestrength or rmagnitude Aof the oscillations by varying'the input capacity-of` from the `grid-cire uitinductance LI and other portions rof theoscillatory-circuit -as-will-hereinafter be ijlescribed.4

PIhe modulatiortsource-for f theeireuit shown in'ilfigure l I n-ay comprise variable--inductance 'elements orother forms-of variable-impedance adapted for connection `bet-Ween the terminal ends fofthe transmission; line -Or-contro1 circuit Aand ground for 'the --system. Furthermore the feediback coupling inductaijiceMA and -they grid -cir- .lation :is yeried., inrespense 4,te Operation Dfithe modulating means thereby ,causingyariatienfof feedfback energy, from -lthe annueeircuit to .the A grid circuit in ,aidiinev or opposing relation with cuit induct-ance` 43,-' that isi-Ll--a1'u;l1-L|,-y may be combined -and connectedv --wth -f-the modulation sour-ce through -the transmission -line ori-control circuit, when the modulation source comprises variable'inductanceielementsilishes and maintains oscillationftherefore lcauses numerals asr'nsEieurel;

'1 In; Figure- By-,it will be see-n;that'the-rnodulation ls ounoe i s 4 of the variable induct-ance'type comprising an nductance Winding# 0' -connfected between thereon-trol lead 5D and--the-ground--return--leads As 'ition Lto befdiierentially pontrolled thymovement Vcirnuit by variation of vthe innutrcapaeity only otanass-ocfrated, ferro-*magnetic core element,-. in-

Adicated atrlr'inresponse toym-ovement-of a modulation member or 'stylus-e 6 4- which in voperation movesiin the direction ofthe arrows.

^ l 11 rection serves tol lincreaseythe impedance of the winding lli while decreasing the impedance of the winding 1l, and in the lopposite direction increases the impedance of .the winding 'Il while correspondingly decreasing the impedance of the winding lil, thereby varying the relative impedances of the Itwo branches of the ycontrol circuit and the feed-back effect as in the proceeding example. i l

The oscillator'end .of the control circuit 50e-5| is connected with terminalsrll and 49 and with the feed-back inductance the two opposing portions '13 and M of which are separated as shown and located in closely coupled relation with the anode inductance 2l at opposite ends thereof. The grid 'l is connected directly to the intermediate or mid-tap point on thek feed-back inductance as indicatedat T5. vSince the inductance elements may all be of the same inductance value and size as referred to hereinbefore, the nductance elements 13 and 'I4 plus :the modulation inductance elements and 'llv respectively, in series therewith to ground and cathode, the grid circuit impedance is therefore provided for without a-ddi-tional in'ductance element. Likewise, the grid resistor and capacitor are eliminated by this arrangement so that the overall circuit is greaty ly simplified.

bined grid circuit reactance reflected over into the oscillator circuit comprising the inductance 21 serves to tune that circuit to the operating frequency ,fl of the oscillator as before.

It has been found that effective modulation by variation of the input capacitance and resultant variation in the strength of oscillation may be provided by the simplified circuit shown. However, the Q of Ll, that is, of the combined inductance of windings 10, 1|, 'I3 and.14 is lower, and the yamount of gain and modulation output 'will be less than when the grid resistor and-capacitor are used. This is forthe reason that the grid leak and capacitor raise the input impedance ofthe tube under a steady state conditionf of oscillation, so that the Q ofrLl, that is, of

`the grid lcircuit inductance, and the associated input circuit will be raised at the resonant frequency. Y

Furthermore, the grid capacitor and e resistor,` when used, provide a time constant lower in fre- As referred to hereinbefore, a portion of the.

circuit of Figure lmay be made -as a detachable unit, including therein the anode circuit and,

feed-back circuit inductances together with the control circuit cable and modulator device.

This unitary arrangement of that portion of Figure 1 is shown in Figure 4, to which attention ,is now directed and in which Vlike reference numerals throughout apply to the same parts as in Figure 1. It will be noted Vthat the anode cir- -cuit inductance L2 and its Vclosely inductively; coupled feed-back inductance coil L3 are in- .number of low cost circuit elementswhich may pedances Vor vreactances of relatively low'value records, has awidel eld of adaptability [and 12 Y e cluded' within a self-contained' circuit "whchis independent of the remainderV of the oscillator system. The coils L2 and L3 are enclosed within a suitable shielded housinguor containervindicated by the dotted' line enclosure 16. f The terminals d8 and 49 of the feed-back in'- ductance winding L3 Vare connected with the leads 50 and 5l through the shielded cablev 52 which is united with the housing creasing whereby the shield is grounded therethrough.

The housing is provided with suitable plug-in terminal pins for the center-tap, terminal 45 of the feed-back Winding as indicated at ll, the terminals vof the anode inductance 2l as indicated at 18, and ground or casing as indicatedat '19. Suitable legends opposite these terminals indicate the corresponding connection points with the circuit of Figure 1. Any suitableterminal arrangement may be provided for plug-in or quick-detachable electrical connection withthe oscillator tube circuit. 'I'he plug-in unitshown in Figure 4 is readily adaptable for vproduction as an article of manufacture for plugging directly into electronic amplier vapparatus containing the remainder of the oscillator circuit, as in the circuit of Figure 1.

From the foregoing description it will be vseen that in accordance with the invention' a self.-

excited, electronic tube oscillator system,V may be provided with high gain, high fidelityl modulation by simplified circuit means providing differential feed-back variation of the input capacitance and response frequency of the grid circuit,

thereby to produce anaccentuated variation 'in the strength of oscillations and in themodulation signal output of the oscil1ator.

This system operates effectively through the medium of a balanced variable impedance feedback circuit 4coupled inductively closely to the anode circuit and having a coupling connection from an intermediate point thereon to the grid circuit. Variable impedancemodulating means in the feed-back circuit provides feed-back current which varies differentially thereby fjto profvide differential in-phase and -counter-phase'inductive feed-back to the grid circuit to vary the amplitude 'of the oscillations and the Vrelative resonant frequencies of the grid andA anode circuits. e Y

The system may be provided by a minimum be combined as shown in Figure 3, and which may bev assembled in substantially a non-.radiating modulated oscillator capable of producinga relatively high gain at the output circuit thereof in response to minute variations of the control element. Y v

Furthermore, because of the eiectivenessof the 'control system, the modulation .source or modulation control elements may comprise imand therefore may be of relativelyV small size and weight as is desirable f or phonograph Vrecord reproduction, for example: An improved electronic tube oscillator system of these1fexcited, modulated*y typel embodying the invention provides a modulation control effect and a modulation voltage or signal output of high fidelity. and

.greatly increased intensity exceeding that ofany known modulated oscillator system, and, accordingly, while particularly well .adapted for faithful and highly amplified'reproduction of phonograph usefulness in the electronic industry.

of the grid-circuit andthe strength :of .oscillations are .varied to efect a variationv inthe-output signal from the-anode circuit at a .modulation frequency,said last named meanscomprising a feed-'back -inductance closely inductively'` coupled to the anode circuit .and having an intermediate terminall connected with the grid circuit, a .pair of= closely associated control leads connectedwith the= terminals of saidv -feed-back...inductance, variableimpeda-nce connected betweenI the .terminal end of each of said leads and ground. for said .d

systemand a movable control element. responsive toy a1 desired modulation frequency for` varying said-1 iinpedances` diiferentially to provide differential -in-phase and counter-phase .inductive feed-back of energy to said gridcircuit to vary the amplitude lof oscillation and the-modulation output -ot said system.

f 2; In an Aelectronic. tubeoscillator.system,the

combination-of means providing a high inductanceanode circuit, a-gridcircuit having a tuning I .inductance therein, means'for variably controlling Aieed-backfof` energy from theanode circuit to. the grid circuit comprising a feed-back inductance `having-close inductive coupling with and a reflected rea'otance in said anode circuit or:tun. ing said oscillator system to a predetermined .oscillation frequency, .means providing. an vintermediatetap connection on said .iced-back. inductanceiorthe grid circuit, means providing a variableimpedance .path between the terminala;v

endsofi-said yfeed-back inductance'and ground .for

lsaid system. operative to eiect. differential conltrol of .said impedance paths,l thereby to provide in.phase and! counter-phase feed-back or energy ltothe grid circuit and a variation.v inthev input `.capacity Aof the gridcircuit, thereby. to vary the strength of .oscillations andthe -anodecurrent proportionally., and means in the .outputfcircuit -of the oscillator'ior deriving therefrom .the.modulationsignal. component.

."SrIn -anf electronic tube oscillatorsystem, the combination of amanodecircuit, agrid circuit, means. foivvariably.controlling feed-back of energy from the anode circuit to the grid circuit comprising aieed-bachyinductance having close inductive: coupling- With and` a `reflected .reaotance in said anode circuit for tuning said oscillator system to a predetermined oscillationfrcquency, means providing a feed-back connection on said induetance for the grid circuit, inodulationgmeans,l

ential modulation control of said impedance paths, thereby to provide differential feed-back variation and a variation in the input capacity of the grid circuit, thereby to vary the strength i oscillations and the anode current proportionally, and means in the output circuit of the oscillator for deriving therefrom the modulation signal component.

4. In a self-excited electronic tube oscillator system having an anode circuit and a grid circuit, the combination with means for establishing ,16o providing a.variablemnedance'nath between the .terminar endsA of .Said feed-back, iindu ctancev and `grammi irorfsad .systempnerative ,to efetgdiiiervaryinertheieed ackfireman@:amdecircmtte the-grida. 1n phase-ane ceunoer-.phasewth respect lzopsaict irjst :named Bell-back A and for varying; tha-.input zcapacityfof; the, grid .circuit and thetuninaresponse; thereof ,f thereby-lio fvary the magnitude orstrength voi "the oscillations Aof the oscillator,` means coupled to theanode circuit .for maintaining-the. frequency-oi the oscillations substantiallyH constant while thetuning response. of the grid circuit fvariesfandgmeans .for derivingan output modulation signal from theanode circuit. 5, In ascii-,excited electronic-.tube .oscillation system, Ainedili-ati ng means therefor. comprising. in combinatiom a grid-circuit tunedtoresonance at apredetermined frequency, r-an.,anode circuit, Aa fecCl-.backqinductance coupled. yto `theE grid circuit from an intermediate-point thereof` and closely inductively coupledyto -thefanode-circuit, means providing atfeed-back pathto grou-nder ,the systern from eachofythe .teitminalsfof said ieedaback inductancefmcans for, idiferentially varyingthe impedance oigsaidfieedfback .paths to pravide ,differentialinmhase andvcoufnter-.phase feed-back of energy; to saidgrid circuit,y to ,vary the `=input admittanoe thereoffand thearnplitude of 4oscillation oiosaidsystem, and means -fordern/ging a modulationfysignal output 4from said ,anode circuit in response.. to. modulation., control vof ,v said .differem .tial;.-=imi:9e0lance lvarying means.

6, In a self-excited..electronic tube.. oscillation system, modulating means therefor.v comprising in combination, a gridcircuittunedto resonanceat a predetermined ,-treuuency,H an` -anode .'circuit, `a ieedfhackv Ainductance included in the .grid y circuit by .connection therewith from. an` intermediate `pointon the feed-back `inductance,said .ieedfback .inductanca-being..closely inductively.- coupled to the anode ycirr-Juit,means ,providing aieed-back path to ground ,of .thesystem fromy eachoithe terminals offsaid feed-@back rinductance, means for idiierentially yarying the-impedance. of .said feedbaclf paths 5to, provide .differential inephase and counter-phaser feed-back of .energy to said .grid lcircuit .to varyfthe input admittance-thereof `and Ithe vamplitude of `oscillation ofsaid system, yand rneansiorderiving a..,modulation ysignal output from said lanode circuit-,in .response to vmodulation .controlof `saiddiii'erential impedance varying means.

'7. An electronic tube oscillator system. compris- :ing inl lcombination va tunable .anode circuit, a l .tunable gridpircuit, an. output anode impedance ,k connected with lsaid tunableanode, circuit, -a third tunable circuit comprising a feed-.back inductance closely, inductivel-y. coupled., with said .anode circuit.and.havingV a midftapl.connectionA coupled. to

`the-grid circuitto applyyariablefeedrback of energythereto, apai-nof -controhleads connected ,with the terminals ofI said feed-backy inductance and extending therefrom `in closelyassociated re- .lation to each'otheuproviding stray capacity between them for tuning said inductance to reso- ,nate .inc .anode Circuit .by .reectecl reactance, means providingl inversely lvariable .impedance elements between the terminal ends of said control leads and ground for said system, means for adjusting the tuning of said anode and grid circuits whereby the frequency of the grid circuit is of the order ci and higher than the frequency of the anode circuit, and means for actuating said variable impedance elements to provide inverse impedance variation thereof to modulate said system.

8. A self-excited electronic tube oscillator sysfeed-back for sustained oscillations, of means for tern comprising in combination, a tunable anode 15 circuit and a tunable lgrid circuit for generating self-oscillations, of a feed-backlwinding closely inductively coupled ton said anode Vcircuit and having a coupling connection from an intermediate point thereon to one side 'of the grid. circuit, means for tuning said feed-back Winding whereby the anode circuit is resonated by reflected reactance therein, saidl means including a control circuit for said winding and a variable impedance element connected with each of the terminal ends of said winding through said control circuit, means for inversely varying said impedance elements to modulate said oscillator system by differentially positive and. negative input'capacity variation on said grid circuit, thereby to vary the strength of said self oscillations, and means for deriving from said system thevmodulation signal resulting from saidl variation.

9. An oscillator system comprising in combination, an electronic tube having an anode, a cathode Yand a control grid, an untuned anode circuit for said tube, an inductance therein, a grid circuit for said tube responsive toa frequency higher than the response frequency of the anode circuit and of the oscillator and having as tuning elements thereof the reflected gridto-anode capacity of said tube and a second inductance, a feed-back circuit, a feed-back inductance in said last named circuit coupled with the grid circuit at substantially the inductive center lof said inductance and having close inductive coupling with the anode circuit, inductance means including'said feed-back inductance providing substantially balanced opposing feedback paths from said grid circuit coupling to ground of said system, means for variablyfunbalancing the impedance of said paths to moduquency higher than the response frequency of the v anode circuit and of the'oscillator and having as tuning elements thereof the reected grid-toanode capacity of said tube and a second inductance, a feed-back circuit, a feed-back inductance in said last namedA circuit coupled With.

the grid circuit at substantially the inductive center of' said inductance and having close inductive coupling with the anode circuit inductance, all of said inductances being substantially equal in inductance value, means including said feed-back;

inductance providing substantially' balanced opposing feed-back paths fromr said grid circuit coupling Vto ground of said system, rmeans for yariably unbalancing the impedance of said paths to modulate said system, and means pro-' viding a modulation signal output circuit for f 11, AnV electronictube oscillatorsystem comprising in combination, means providingr a tunf pedance elements between the louter terminal.

vtion of said system.

able anode circuit inductance and a tunablelg'rid circuit adapted to be coupled and4 tuned bythe inter-electrodal capacities of an associated electronic oscillator tube, an output anode impedance connected with said tunable anode circuit, a third tunable circuit comprising an inductance winding closely coupled with said anode circuit and having a. mid-tap connection thereon coupledto the grid circuit to apply variable current under neutralization thereto, a pair of control 'leads connected with the terminalsy 'of said inductive winding and extendingrtherefrom in closelyasf sociated relation to each other providing stray capacity between them for tuning vsaid inductance to resonate the anode circuit by reectedreactance,rmeans providing inversely variable imends of said control leads and ground for said system, means for adjusting the tuning Vof said anode and grid circuits whereby the frequency of the grid circuit is higher than the frequency of the anode circuit, and means for actuating said variable impedance elements to provideinverse impedance variation thereof and modula- 12. A self-contained modulator lunit forl an electronic tube oscillator system comprising in combination, a pair of closely coupled inductance coils, a transmission system having ,a pair of conductors respectively connected tothe end terminals of one of said inductance coils and being adapted for connection at their outer terminal ends to a pair of impedances, said transmission system conductors being relatively immovable with respect to one another throughout the major extent of their length, a conductor connected to an intermediate point of that one of said inductance coils which is connected to the rtrans-'- mission system conductors, said pair of inductance coils andsaid transmission system conductors being enclosed withinan electrically conductive shield and said impedances being reof an electronic tube oscillator system to be modfile of this patent:

`UNITED STATES PATENTS Number Name Date 2,009,069 Pray July 23,` 1935 2,160,466 Usselmann May 30, 1939 2,288,486

Rivlin Junev30, 1942y Certificate of Correction Patent No. 2,443,125. June 8, 1948.

PAUL WEATHERS It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Column 1, line 7, for the patent number 2,436,139 read 2,436,129; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 7th day of September, A. D. 1948.

[SEAL] THOMAS F. MURPHY,

Assistant Uommz'ssz'oner of Patents. 

